Translucent plastic foam
This Answer is incomplete, but might bring you closer to your goal.



I used a Volume shader hooked up to a voronoi texture to create the bubbles, but I didn't manage to make them glossy or refractive.
Is that even possible, using volumes?

The biggest problems with your render are:


it is only one closed volume, it will never give realistic results 
don't use emission shaders in non-emissive materials


With materials like this, I would strongly recommend using a completely procedural way, without any image textures.